EXCITON-EXCITON ANNIHILATION IN POLY(P-PHENYLENEVINYLENE) FILMS

We have measured the saturation of fluorescence intensity with increas ing excitation intensity and the time dependence of fluorescence inten sity decay at high excitation intensities in poly (p-phenylenevinylene ) films. The experimental results are consistent with the hypothesis t hat exciton-exciton annihilation reduces the exciton lifetime at high exciton concentrations and that the exciton diffusion coefficient is q uite high. We conclude that the lowest energy electronic transition cr eates a Frenkel exciton rather than a free-carrier pair in a band-to-b and transition.